In a paper board such as a container board, most of the raw material is comprised of waste paper.
In producing a paper board using waste paper as a main raw material, a paper board is produced through a pulping step of disintegrating and beating fibers from a pulp raw material with a pulper using waste paper as a main raw material to obtain a pulp slurry (also referred herein as “pulping process water”) first; and then a stock preparation step of adding an additive containing a paper strength additive to the obtained pulping process water to obtain a prepared pulp raw material; and paper-making step of making the obtained prepared pulp raw material into a paper board. In the stock preparation step, a paper strength additive is added to the stock preparation water in order to keep the strength of the obtained paper board.
Waste paper contains a lot of starch from an adhesive or the like.
For this reason, Japanese Unexamined Patent Publication No. 2010-100945 proposes a method of producing the paper wherein the amylase activity, starch concentration, pH and oxidation reduction potential of the process water are continuously or intermittently measured and a bactericide is added due to the result of the measurement in order to prevent the degradation of starch in the pulping process water of waste paper on the assumption that the degradation of starch is caused by putrefaction due to the proliferation of microorganisms.
Japanese Unexamined Patent Publication No. 2011-226043 concludes, however, that the direct addition of a bactericide to the pulping process water of waste paper causes only partial disinfection with insufficient disinfection effect because of the poor dispersibility of the bactericide, the pulping process water having high pulp concentration not less than 3%. In other words, Patent document 2 concludes that the method of Patent document 1 cannot fully suppress the deterioration of the quality of the paper caused by microorganisms. Thus, Patent document 2 proposes a method of suppressing slime by adding a bactericide to diluent water for diluting the raw material in the process of producing the paper using waste paper or the like as raw material.